One category of high-capacity storage batteries that store new energy such as solar power and wind power is electrolyte-circulating batteries whose representative example is redox flow batteries (RF batteries). RF batteries are a type of batteries that are charged and discharged by utilizing the difference in redox potential between the ions contained in the positive electrode electrolyte and ions contained in the negative electrode electrolyte (for example, refer to PTL 1). As illustrated in an operation principle diagram of an RF battery 1 in FIG. 15, the RF battery 1 includes a battery cell 100 that includes a positive electrode cell 102 and a negative electrode cell 103 separated from each other by a hydrogen-ion-permeable membrane 101. The positive electrode cell 102 includes a positive electrode 104 built therein and a positive electrode electrolyte tank 106 that stores the positive electrode electrolyte is connected to the positive electrode cell 102 via ducts 108 and 110. A pump 112 is connected to the duct 108. These components denoted by 106, 108, 110, and 112 constitute a positive electrode circulation mechanism 100P configured to circulate the positive electrode electrolyte. Similarly, the negative electrode cell 103 includes a negative electrode 105 built therein and a negative electrode electrolyte tank 107 that stores the negative electrode electrolyte is connected to the negative electrode cell 103 via ducts 109 and 111. A pump 113 is connected to the duct 109. These components denoted by 107, 109, 111, and 113 constitute a negative electrode circulation mechanism 100N configured to circulate the negative electrode electrolyte. The electrolytes stored in the tanks 106 and 107 are circulated into the cells 102 and 103 by the pumps 112 and 113 during charge and discharge. When neither charge nor discharge is being conducted, the pumps 112 and 113 stop operation and the electrolytes are not circulated.
In general, the battery cell 100 is formed inside a structure called a battery cell stack 200 such as one shown in FIG. 16. The battery cell stack 200 is prepared by sandwiching a stack structure called a substack 200s between two end plates 210 and 220 on the both sides and clamping them together by a clamping mechanism 230 (the structure illustrated in the drawing uses plural substacks 200s). As shown in the upper part of FIG. 16, the substack 200s is prepared by stacking cell units each including a cell frame 120, a positive electrode 104, a membrane 101, a negative electrode 105, and another cell frame 120 and sandwiching the stacked cell units between supply/discharge plates 190 and 190 (refer to the lower part of FIG. 16). Each of the cell frames 120 in the cell unit has a frame body 122 that has a penetrating window and a bipolar plate 121 that fills the penetrating window. The positive electrode 104 is arranged to contact a first surface side of the bipolar plate 121 and the negative electrode 105 is arranged to contact a second surface side of the bipolar plate 121. According to this configuration, one battery cell 100 is formed between the bipolar plates 121 of the adjacent cell frames 120.
Distribution of the electrolytes to the battery cell 100 via the supply/discharge plates 190 and 190 of the substack 200s is performed through liquid supplying manifolds 123 and 124 and liquid discharging manifolds 125 and 126 formed in the frame bodies 122. The positive electrode electrolyte is supplied to the positive electrode 104 from the liquid supplying manifold 123 via an inlet slit formed in the first surface side (the front side of the plane of the paper of the drawing) of the frame body 122 and discharged to the liquid discharging manifold 125 via an outlet slit formed in an upper portion of the frame body 122. Similarly, the negative electrode electrolyte is supplied to the negative electrode 105 from the liquid supplying manifold 124 via an inlet slit (shown by dotted lines) formed in the second surface side (the rear side of the plane of the paper of the drawing) of the frame body 122 and is discharged to the liquid discharging manifold 126 via an outlet slit (shown by dotted lines) formed in an upper portion of the frame body 122. A ring-shaped seal member 127 such as an O-ring or a flat packing is placed between the cell frames 120 to suppress leakage of the electrolytes from the substack 200s. 
Input and output of power between an external device and the battery cell 100 in the substack 200s are achieved by a current-collecting structure that uses current collector plates formed of a conductive material. One pair of current collector plates is provided for each substack 200s, and the current collector plates are respectively electrically connected to the bipolar plates 121 of two cell frames 120 located at two ends in the stacking direction among the stacked cell frames 120.